According to the ratiometric dual slope analog-to-digital conversion technique known to the art, the level of an unknown analog signal is measured by integration thereof over a precise time interval. Upon completion of this measurement integration cycle, the resultant value is integrated with respect to a sensed external reference value of a polarity which causes the resultant value to decrease at a constant rate. The interval of time required for the resultant value to return to zero or its value prior to the measurement integration cycle is measured by appropriate counter and clock means to provide a digital indication of the analog input value. According to this conversion technique, the measurement integration cycle and the reference integration cycle occur sequentially and is susceptible to non-periodic and short term noise.